1. Field of the Invention
The present invention relates to a nonreciprocal circuit device such as an isolator and a circulator used in a high frequency band such as a microwave band.
2. Description of the Related Art
This type of the nonreciprocal circuit device includes a magnetic assembly 50 having a structure shown in, for example, FIG. 13. The magnetic assembly 50 is composed of a magnetic body 55 composed of a rectangular plate-shaped ferrite, a common electrode 54 composed of a metal plate and disposed on the lower surface of the magnetic body 55, and a first central conductor 51, a second central conductor 52, and a third central conductor 53 which extend radially from the common electrode 54 in three directions and are wound on the front surface side of the magnetic body 55.
The first, second, and third central conductors 51, 52, and 53 are bent along the magnetic body 55 and overlapped each other at an intersecting angle of about 120° on the front surface of the magnetic body 55. Note that, while omitted in the figure, the central conductors 51, 52, and 53 are individually insulated from each other by insulation sheets on the front surface of the magnetic body 55.
Further, each of three central conductors 51, 52, and 53 is disposed such that the extreme end thereof extends from a side of the magnetic body 55, and the extreme ends of the central conductors 51, 52, and 53 are arranged as respective ports P1, P2, and P3. Then, the nonreciprocal circuit device is arranged such that a not shown matching capacitor is connected to each of the ports P1, P2, and P3, a terminal resistor is connected to one of the ports through the capacitor, and they are accommodated in a magnetic yoke, which constitutes a magnetic circuit, together with a permanent magnet so that a DC magnetic field can be applied to the magnetic assembly 50 by a permanent magnet disposed separately.
As shown in a developed view of FIG. 14, the respective central conductors 51-53 are mutually connected and integrated at the common electrode 54 acting as a ground portion and extend from the common electrode 54 in the three directions. These central conductors 51 to 53 are bent at the positions of bending portions X shown in FIG. 14 so that they are accurately assembled to the magnetic body 55 at predetermined angles.
In the nonreciprocal circuit device having the conventional arrangement, the accuracy with which the central conductors 51-53 are assembled to the magnetic body 55, the intervals between the conductors, and the intersecting angles of the central conductors are important factors for determining the electric characteristics of the nonreciprocal circuit device, and even a slight variation of the values of them from designed values deteriorates the performance of the nonreciprocal circuit device.
In particular, this type of the nonreciprocal circuit device has an overall size of a 4 to 5 mm square to cope with the recent miniaturization of a high frequency circuit. However, it is very difficult in the magnetic assembly 50 having the structure shown in FIG. 13 to strictly adjust the assembling accuracy of the central conductors 51 to 53 to the magnetic body 55, the intervals between the conductors, and the intersecting angles in such a minute part.
For example, in the magnetic assembly 50 having the conventional arrangement, the central conductors 51 to 53 must be disposed on the magnetic body 55 by being accurately bent at the positions of the bending portions X shown in FIG. 14 along the sides of the magnetic body 55. However, even a slight dislocation of the positions of the bending portions X of the central conductors 51 to 53 in the isolator having the overall size of the 4 to 5 mm square greatly varies the intersecting angles of the central conductors 51 to 53 that intersect on the front surface of the magnetic body 55. Further, the bending portions X of the central conductors 51 to 53 must be accurately aligned along the edges of the sides of the magnetic body 55 and carefully bent, which deteriorates workability when the magnetic assembly 50 is assembled.